what is the wrong in the code?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace function_of_product
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("x=");
            Console.Write("y=");
            int x = int.Parse(Console.ReadLine());
            int y = int.Parse(Console.ReadLine());
            int tot = multi(x, y);
            Console.WriteLine("tot=" + res);
            Console.ReadKey();
        }
        static int multi(int x, int y);
 
        int res = x * y;
        Return (res);
 

    }
}